1. Field of the Invention
The present invention relates to a lens barrel mounted on an image pickup apparatus such as a camera, and more particularly relates to a lens barrel including a barrel member that linearly advances/retracts in the direction of an optical axis of the image pickup apparatus.
2. Description of the Related Art
Some lens barrels for image pickup apparatuses may include a zooming mechanism, and the zooming mechanism includes a linear movement mechanism configured to move the lens barrel in an optical axis direction of the image pickup apparatus from a retracted position at which the lens barrel is housed in a body of the image pickup apparatus to a shooting position without turning the lens barrel.
Conventionally, the linear movement mechanism employed in the lens barrel may include a type of guiding a linear movement barrel with respect to a fixed barrel linearly in the optical axis direction by means of interaction between a linear movement key formed on the linear movement barrel and a linear movement groove formed on the fixed barrel. In such a linear movement mechanism, if the linear movement groove is formed on the fixed barrel over the entire region from the retracted region to the shooting region, the linear movement groove crosses a cam groove and/or a through groove formed on the fixed barrel, thereby unfavorably disabling the linear movement barrel to be guided linearly.
Therefore, in such a linear movement mechanism, the fixed barrel has a first and a second linear movement groove formed in the shooting region and the retracted region, respectively, and also the linear movement barrel has a first and a second linear movement key formed in the retracted region and the shooting region; accordingly, changing the engagement of the linear movement key to the linear movement groove allows the linear movement barrel to be guided linearly in the optical axis direction. Furthermore, according to the linear movement mechanism, the first linear movement key formed on the linear movement barrel engages with the first linear movement groove formed on the fixed barrel in the shooting region while disengaging with the first linear movement groove with a little backlash in the retracted region, whereas the second linear movement key formed on the linear movement barrel engages with the second linear movement groove formed on the fixed barrel in the retracted region while disengaging with the second linear movement groove with a little backlash in the shooting region (see Japanese Laid-Open Patent Publication (Kokai) No. 2010-048967, for example).
However, in the aforementioned structure of the linear movement mechanism, the cam groove and/or the through groove formed on the fixed barrel restricts the shape of the linear movement key, thereby making it difficult to ensure the rigidity of the linear movement key.
Furthermore, if the linear movement barrel receives a torque upon receipt of the impact of, e.g., dropping, the torque generated by the impact is imposed on the first linear movement key and the first linear movement groove engaging with each other. Furthermore, if the torque generated by the impact is so large as to deform the fixed barrel, the second linear movement key and the second linear movement groove disengaging with each other, also receive the torque.
If the second linear movement key is located on a part of the second linear movement groove crossing the cam groove and/or the through groove, the linear movement barrel receiving a larger torque due to the impact allows only the first linear movement key and the first linear movement groove to receive the torque, thereby resulting in the turning force concentrating on the first linear movement key, which may cause a failure if the linear movement key cannot be provided with ensured rigidity.